This invention relates to dry shavers of the kind having an inner cutter adapted to be driven in linear reciprocation beneath a cutting foil by drive means including a driver articulated to the body of the inner cutter which carries the cutting blades cooperating with the foil.
In a dry shaver of the kind described, the cutting blades and the foil are biassed into engagement, usually by means of a spring acting on the cutter body along an axis through the center of gravity of the inner cutter perpendicular to the direction of reciprocation. In consequence, during operation of the shaver, frictional forces are developed between the foil and the inner cutter. These frictional forces vary in magnitude when the shaver is in use for shaving. However, the line of action thereof is found to be constant, and lies parallel to the direction of reciprocation. Moreover, the center of application of the resultant of these frictional forces is found to be fixed, and lies on the above-mentioned axis through the center of gravity of the cutter perpendicular to the direction of reciprocation. The present invention stems from an appreciation of the significance of these frictional forces in causing uneven wear and increasing power consumption, and in a consequent analysis of the magnitude and center of application of the resultant of the frictional forces.
In addition, in use of the shaver the inner cutter is subject to inertial forces of acceleration varying sinusoidally in known manner. The line of action of these inertial forces is also parallel to the direction of reciprocation, and the center of action of their resultant is at the center of gravity.